Apparatus for sealing-off electric discharge tubes



Dec. 5, 1950 w. A. ROOVERS ETAL ,86

APPARATUS FOR SEALING-OFF ELECTRIC DISCHARGE TUBES Filed Dec. 22, 1948 3 Sheets-Sheet 1 TORS W.A. RooyeRs C. F. VEE,NEMANS 0.1.. VAN STEENIS Filed D 22' 1948 W. A. ROOVERS ETAL APPARATUS FOR SEALING-OFF ELECTRICDISCHARGE TUBES 3 SheetS-Sheei-Z W. A. :C.F. VEE

2 AGENT IN VEN TORS ROOVER NEMAN ENIS Dec. 5, 1950. w. A. ROOVERS ET'AL 2,532,

APPARATUS FOR SEALING-OFF ELECTRIC DISCHARGE TUBES fiiiled Dec. 22, 1948 s Sheets-Sheet s oooodoodi 5 i I 00000000; l oooooooo WA. ROOVERS C.F. VEENEMANS Q LyvANzE BY Patented Dec. 5, 19 50 APPARATUS FOR SEALING-OFF ELECTRIC DISCHARGE TUBES Wilhelmus Antonius Roovers, Cornelis Frederik Veenemans, and Otto Louis van Steenis, Eindhoven, Netherlands, assignors to Hartford National Bank and Trust Company, Hartford,

. Conn., as trustee Application December 22, 1948, Serial No. 66,638

, In the Netherlands January 22, 1948 This invention relates to'apparatus for sealing-off the exhaust tube of electric discharge tubes, which exhaust tube passes through a bottom disc into which the contact pins are also sealed. In such discharge tubes the exhaust tube provided in the said disc, is sealed oif by means of gas flames while the discharge tube is rotated. In this event the sealing off of the exhaust tube should be effected at a-distance from the bottom of the tube exceeding the length of the contact pins since otherwise the latter are excessively heated by the gas flames with the concomitant disadvantages, for example oxidation of the pins and consequently deficient contact in the holder and cracking of the glass bottom of the tube. For this reason it is necessary to protect the exhaust tube after the sealing operation, which is generally effected by means of a bush acting at the same time as a centering pin and as location lug and being secured to the bottom by means of a screen plate. However, this construction is comparatively expensive and involves losses at very high frequencies. Moreover, such a construction occupies too much space for use with small-size tubes and the overall length of the tube is increased due to the portion of the exhaust tube projecting below the plus. r

To permit the exhaust tube to be sealed-off. as near as possible to the bottom special precautions must be taken in order to avoid excessive heating of the pins. For example, British patent specification 559,753 describes a method for achieving this. In order to avoid the dim-- culty of excessive heating of the pins, the rotation of the tube may be interrupted and the exhaust tube may be sealed-off by means of small sharpl pointed flames playing between two pins. Since, however, the flames must be very small the sealing operationoccupies too much time. According to the said British patent specification this disadvantage is avoided by sealing by means of an electrically heated heating coil. The tube is placed on a table and the pins engage apertures of an insulating member, several apertures being provided with contact members for the supply of current to the electrodes, for example the filament of the cathode. By providin cooling channels excessive heatin of the pins and the bottom of the tube is prevented on sealing oil? the exhaust tube. The sealing operation is efiected by means of a large heating coil closely surrounding the exhaust tube in a cavity which is provided in the insulating body within the pins. Upon softening of the glass of the exhaust tube- 3 Claims. (01. 49-2) 2 the table is moved upward owing to -which the exhaust tube is drawn out to a capillary and becomes sealed.

However, the use of a heating coil for sealing off the exhaust tube involves serious disadvantages.

Thus, for example the surroundings of the heating coil are strongly heated, so that complicated cooling ducts must be provided for the. contactpins and this is made more diificult by the fact that these pins are provided in an insulating body having a low thermal conductivity. Owing to this it is difficult to interrupt the heating operation of the exhaust tube at given instant to prevent suckin in of the glass of the exhaust tube.

Furthermore, the filament must be strongly heated after drawing out the exhaust tube, since the spacing'between the filament and the glass of the exhaust tube has considerably increased. This sooncauses deformation and oxidation of the heating coil, so that it must be repeatedly renewed. In addition, a serious drawback consists in that the strong heating current for this heating coil must be supplied through sliders at a low voltage so that large contact rails and brushes are required. Thereby the construction of the table is comparatively complicated. Since the exhaustion and sealing of the tube is generally effected in arotary machine with 30 positions, 30 tables each comprising a heating element are required for operating the machine at full capacity.

For all that, it has been found possible to use gas flames for sealing the exhaust tube rapidly, whilst avoiding the aforesaid disadvantages.

According to the invention this is ensured in a device for sealing ofi the exhaust tube of an electric discharge tube closed by a bottom disc into which the exhaust tube and contact pins are sealed, by placing the tube in a metal holder provided with apertures for receiving the contact pins and for the passage of the exhaust tube, in which last-mentioned aperture one or more radial slots empty, of which the width, at least over part of them, is smaller than the spacing between two contact pins and each of which extends between two pins closely below the bottom of the tube the slots being provided with at least one partition and the exhaust tube being sealed off through them by means of flames at a distance from the bottom of the tube smaller than the length of the contact pins. It has been found that in spite of the. small width of each slot the gas flames are able to penetrate to the exhaust tube, although the side walls of the slots,

which walls may be parallel or at an angle to one another, consist of metal, preferably copper.

In a device according to the invention the exhaust tube, similarly to, the said British. patent. specification 559,753, is; drawn outto. a capillary upon softening. Owing to the partition in each slot, which partition extends parallel with the. bottom of the tube in this case the capillary part can be sealed ofi without heating the remaining. glass of the exhaust tube, with the result that sucking in of the glass of the exhaust. tube is. avoided. Since the holder orthe tubemay practically entirely consist of metal, the heat is carried ofi sufficiently, so that intricatescoolingchannels may be dispensed with. If several pins must be connected to supply contacts. for the. supply of current to an electrode, for example. the filament. of the cathode, the apertures for these pins may have a larger diameter so that these pins extend freely through these apertures and engage the a contact members.

Consequently, the. device of; our invention may have a very simple construction. Since. the: slots for the sealing flames are. usually narrower than the diameter of the exhaust tube rapidxsealing of the exhaust tube seemed impossible in the aforee saidmanner. With the use'of oxygen gas flames, however, the exhaust, tube can be. heated. sulficiently rapidly. Since the oxygen flames, upon traversing the slots; directly reach the exhaust tube, the. latter will be heated rapidly, it. is: true, but at th same timeunevenly, so thatthe burn:- ers must be. adjusted very' accurately inz order: to avoidlocal. overheating and consequently sucking in of the glass ofthe exhaustttube. This. difficulty can be avoided by providing a separately perforated screen which extends in each slot at right. angles to the bottom of the tube:,.so that the combustion gases of the sealing; flames. pass. more evenly around the heated part of the exhaust tube, and this part is evenly. heated; As: a result thereof, the risk of. sucking in ofcertain. glass parts due to local overheating isconsiderr ably reduced, so that the adjustmentofthe burn.- ers has less influence on the temperature of the glass.

: In order that the invention may. bemorewlear- 1y understood and readily carriediinto efiect, it will now be described more fully with reference; to the. accompanying drawings given by: wayxofi example in which Fig. 1 is an elevational view partly in? section of: a sealing-oil apparatus showing the initial: heating of the. exhaust tube. priorto sealing-oi;

Fig. 2'is a view. similar tothatof Fig. I showing th position. of the. apparatus: of invention when the. exhaust tube. has been extended. to. form a. capillary;

Fig. 3 is a view. similar to. that. ofiFigs. 1' and 2.: showing the exhaust tube. separated; at; the. cat-nil,- lary by the action. of. the tensioningdevice;

Fig. 4. is a view partly in section takenonzlinez IV-IV of Fi 3;.

Fig, 5 is. aview partly in section takenonzline VV of- Fig. 3;

Fig, 6. is a side. elevational view; of thetubeand: holder of-Figs. l, 2'and 3;.

Fig. '7 is;.a bottomend view oftherapparatus of Fi 6;

Fig. 8. is an elevational view. ofra screenused in. a further embodiment of theinventioniorsecur. ing uniform heatingof theexhaust tube;

Fig. 9 is a view of. a portion of azholden similar tov Fig. 4 and embodying. the; screen of Fig. 8;

In Fig. 1 the discharge. tube;- I comprising-5a.

- tures 40 and are provided with contact members 9 and. It whichare. secured to an insulating plate flandserve to supply heating current to the heating member of. the cathode of tube I. The pins 3Jdo. not contact. the Walls of the apertures 38 and 39 of larger. diameter.

The exhaust tube 4 is placed in a stop cook 12 (Figs... 1-3) and thus connected to a vacuum pump. The stop cock i2 is secured to an annular frame.- i3'- usually carrying 30 tube holders 6 corresponding with 30 positions which are traversed during one revolution of theframe i3.

The stay rods H are provided. with a roller l4 passing in the. aforesaid positions over a guide I5. This guide I5 is. rotatable about abolt l6 and is moved upward bya spring; I 7 against a stop 18 Th spring ll has. such a tension. as to be com.- pressedwhen theroll'er I4 passes overthe guide l5.

actionof. spring I 1. heated and softens (Fig. 1)- thespring'forcedominates,,so that. the holder 6' secured to the rod H.

is moved upward by the spring I! through. the

flames which. are directed. by burners 2| just.

through the slots. 1.90:. of the member 5. In this construction a member T exhibiting slots i922 which are'separated from the-slots I921 by a metalpartition 26, if. desired perforated, is clamped against the underside of. the member 5.. The flames. pass. through the narrow: slots 19a. and. heat the.- exhaust tube ll'- Although the slots [Hm are very narrow at least over part of them, name.- ly narrower thanthe spacing. between two contact pins 3 of tube i, it. appears: thatthe gas flames. readily. pass through these; slots so that the: exhaust tube 4is heated and softened rapidly the exhaust. tube being drawn out to a capillary at. the heated area as described above, as a result.

of whichthe assembly occupiestheposition shown. in Fig... 2. Immediately upon drawing; out. to. a.-

capillary the. tubeis moved" to the position shown; in Fig. 3-, so that; the flames of; the burners 2|. finding their." way below the. partition 20 upon. moving the: tube, upward, are unable, to seal the.

exhaust tube. completely. Owing tothe bi-lateral.

and consequently uneven heating of? the exhaust. tube parts of the exhaust; tube might then. be sucked in, due to which the. open air could pens-- trate into the vacuum. space. For this. reason the sealing: of thecapillary exhaust tube is effect.- ed? in the next position (Fig. 3) by means of a: flame. from the burner-Z2 directed exactly along the underside. of the partition 29; Gn passing, overfronr theaposition shown inFigs. 1 and 2 to thatsliown. in Fig.3. the. part. of:the exhaust tube.- connected to. the bottom of the tube is cooled sufliciently" to avoid sucking. in. on. sealing the capillary. In. this manner-the well-known sealing tip;23.isfiormedatthebottomend of the tube.

The holder 6 and its associated parts are normally held by the exhaust: tube 4' against the- If the exhaust tube is locally I, but this tip is shorter than the length of the contact pins 3, so that it is protected by these pins against mechanical damage. Figs. 4 and 5 clearly show the small width of the slot 19. Notwithstanding that the sealing operation can be effected rapidly so that 1000 tubes can be exhausted per hour.

In another embodiment a separate perforated screen 24 (Fig. 8) is provided. This screen is placed between the flames and the exhaust tube 4. In this manner the exhaust tube 4 is evenly heated so that the surrounding mass softens simultaneously and the risk of sucking in of overheated glass parts is greatly reduced. In this event the force required for drawing out the tube by the device as shown in Figs. 1 and 3 need only be exerted after the glass has become soft so that there is no risk of the tube being pulled from the exhaust tube, as in the first-mentioned case. The upward force is exerted on the table only after the sealing operation of the exhaust tube. The screen 24 is provided with apertures 25 and. 26 which in the present case, have diameters of 0.5 mm. and 0.45 mm. respectively. The number and the diameter of these apertures may be changed according to want. Though the screen 24 becomes hot, it cools rapidly on passing over to the next position of the holder, due to the considerable dissipation of heat through the metal holder. This is not the case with the use of an insulating member as used in British patent specification 559,753. The risk of further softening of the glass after removal from the flames is consequently very small, since practically no afterheating by the hot screen occurs. Furthermore, the provision of separate ducts for cooling air to keep the bottom of the tube and the contact pins sufiiciently cool is rendered superfluous by the rapid dissipation of heat through the metal member 5 according to the invention.

What we claim is:

1. An apparatus for sealing-off an electric discharge tube having an envelope including contact pins and an exhaust tube which extend from the said envelope in substantially parallel relation, comprising a metal tube holder having spaced elongated recesses adapted for receiving said contact pins and a passageway adapted for receiving said exhaust tube and also having radial slots extending from the periphery of said holder inwardly to said passageway, said slots being positioned between said recesses and above the lower ends thereof and having a width less than the said spacing between the said recesses, and a partition in said slots forming separate passages therein and adapted to receive heating flames selectively from burners in alignment with said slots at the outer periphery of said tube holder.

2. An apparatus for sealing-off an electric discharge tube having an envelope including contact pins of a given length and spacing and an exhaust tube extending from said envelope in substantially parallel relation, comprising a metal tube holder supporting said discharge tube thereon and having spaced elongated recesses therein for the positioning of said contact pins and a passageway for said exhaust tube, said holder also having radial slots therein extending from the periphery of said holder inwardly to said passageway at a distance below said envelope of less than the said length of the said contact pins, said slots being positioned between and having a Width less than the said spacing between the said contact pins, a horizontal partition in said slots forming separate passages longitudinally therein, and burners positioned at said slots at the periphery of said. tube holder to apply flames to said exhaust tube through said slots to seal-ofl said envelope.

3. An apparatus for sealing-off an electric discharge tube as claimed in claim 1,- in which a vertical perforated screen is provided at the area where the slot extends to the passageway provided in the holder for the passage of the exhaust tube.

WILI-IELMUS ANTONIUS ROOVERS. CORNELIS FREDERIK VEENEMANS. OTTO LOUIS VAN STEENIS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,215,100 Gustin Sept. 17, 1940 2,273,445 McGowan et al. Feb. 17, 1942 2,278,500 Smith Apr. 7, 1942 2,434,664 Malloy Jan. 20, 1948 

